Joined arc carbons



April 11, 1967 w. R. LAUZAU ETAL 3,313,976

JOINED ARC CARBONS Filed Oct. 18, 1963 INVENTORS WILBUR R.LAUZAU MARVIN R.RIEK

ATTORNEY United States Patent 3,313,976 JOINED ARC CARBONS Wilbur R. Lauzau and Marvin R. Riek, Fostoria, Ohio, assignors to Union Carbide Corporation, a corporation of New York Filed Oct. 18, 1963, Ser. No. 317,339 9 Claims. (Cl. 313-354) This invention concerns a treatment for joined arc carbons which provides smooth operation during the period in which an arc burns through the joint between the carbons.

It is desirable to improve arc lamps by extending the period in which they can operate continuously. Arc lamps employed for solar simulation or for illuminating movie screens are particular examples in which longer operation is needed. One method of extending the period of continuous operation is to join an arc carbon in an end-toend relationship with the arc carbon immediately in the arc and continually adding arc carbons in this manner for as long as continuous operation is desirable. In this method, however, the arc is sometimes unsteady while the joint between the arc carbons is in or near the are. This effect is obviously undesirable since the radiation emitting from the arc is likewise unsteady. For uses such as solar simulation in which a very steady arc is required, this effect is disadvantageous.

The principal object of the invention therefore is to provide an arc carbon which may be joined to another are carbon to form an assembly of carbons which may be fed into an arc with a minimum of arc unsteadiness during the period in which the joint between two arc carbons is burning in the are.

A sectional view of an arc carbon assembly embodying the features of the invention is shown in the accompanying drawing.

Broadly stated, the above object is achieved by an arc carbon electrode having a plug on one end and a socket in the other end, thereby being adapted to be a member of a series of arc carbons assembled end-to-end, and an arc-supporting material disposed either in the socket or on the end of the plug which helps to maintain a steady arc during the period in which the joint between two carbons burns. As used herein, the term arc-supporting material refers to a material which when placed in the joint between two joined arc carbons depresses the arc voltage otherwise obtained during the period in which the joint burns in the are. When the carbon electrodes are formed into an assembly of arc carbons suitable for use in an arc lamp, the are supporting material is disposed in the socket of one electrode between the plug of the other electrode and the socket wall.

In accordance with the invention, the assembly of arc carbon electrodes shown in the drawing comprises a first carbon electrode 10 joined to a second carbon electrode 12. Each of the carbon electrodes 10 and 12 are positive arc carbon electrodes since the invention is particularly advantageous when employed with respect to positive arc carbon electrodes. Each of the electrodes 10 and 12 comprises a shell 14 composed principally of carbonaceous material, such as graphite, and a core 16 inside the shell 14 principally composed of carbonaceous material and a flame material. As used herein, the term flame material refers to a material which upon excitation by electrons in an arc yields highly luminescent radiation. Flame materials in general use include the oxides and fluorides of rare earth metals such as cerium and may also be metals such as thorium, iron, nickel, cobalt, manganese, strontium, calcium and vanadium. Compounds other than oxides and fluorides of the rare earth metals may also be employed, and such techniques are known in the art.

An arc carbon electrode as shown may be easily made by extruding a core mix, baking the mix, and then inserting the baked core with a suitable binder therearound into a baked shell to form the final arc carbon electrode. The baked shell is preferably formed by mixing carbonaceous material with suitable binders, extruding the mix in the form of a shell, and then baking the shell in accordance with conventional procedures.

As shown in the drawing, each of the carbon electrodes 10 and 12 have a socket 18 in one end and a plug 20 on the other end adapted to fit in the socket 18-. The plug 20 and socket 18 on adjacent electrodes may be engaged by a force fit or by mutually engaging threads as shown in the drawing. Another technique employed in joining arc carbons is to provide a cement, preferably a carbonizable cement such as phenol-formaldehyde resin, in the joint between the joined arc carbons to bond and join the arc carbons together.

In accordance with the invention, an arc-supporting material 22 is disposed between the plug 20 and the socket 18 in which the plug 20 fits. The arc-supporting material 22 may be merely disposed loosely in the joint, but is preferably bonded to either the plug 20 or the socket 18 by a suitable cement, for example a solution of sugar in water or a solution of phenol-formaldehyde resin in all organic solvent such as acetone or butanone. A cement which includes a solvent is preferred since such cements usually set more readily.

The arc-supporting material is preferably potassium sulfate but may also be calcium fluoride, sodium sulfate, silicon metal or mixtures of these materials. The aresupporting material need be present in only a very small amount, but should be present in an amount which provides substantially steady arc operation. If too much of the material is added to a joint, the arc voltage will be depressed too much with consequent excessive loss of light while the joint is in the arc. Theoretically the arcsupporting material should be added in an amount which provides a voltage during joint burning substantially equivalent to the voltage of the arc when the joint is not in the arc. Carbons of a different size require slightly different amounts of the arc-supporting materials for optimum results shown in Table I below:

TABLE I.PREFERRED AMOUNTS OF ARC-SUPPORTING MATERIAL IN JOINT BETWEEN ARC CARBONS Operating Current, amps.

Carbon Joint Treatment 2S 4. 350400 0.04-0.05 gram,

13.6 mm. High Intensity, Positive.

16 mm. High Intensity, Positive An arc carbon assembly in accordance with the invention has performed very well in an arc lamp and has provided substantially steady arc operation during burning of the joint. For example, two positive electrodes of conventional design having a shell of carbonaceous material and a core therein comprising a mixture of rare earth oxides and fluorides, and having a plug and socket on opposite ends with mating threads, were joined together after 0.03 gram of potassium sulfate was spread evenly over the bottom of the socket. The potassium sulfate was held in place by a few drops of a cement consisting of phenol-formaldehyde resin dissolved in acetone. This electrode assembly was then tested in a lamp in arcing relationship with a copper-plated negative carbon of con- Ventional design.

For comparison, another electrode assembly of the same type was prepared and tested but without the additional of potassium sulfate to the joint. Both of the electrode assemblies operated at about 68 volts during the time the solid portion of the positive electrode assembly outside the joint was burning in the are. As the joint in the electrode assembly without the addition of potassium sulfate entered the are, however, the voltage rose to 70 volts and an overload condition was evidenced by a sudden voltage drop and current rise accompanied by squealing of the arc.

With the electrode assembly having potassium sulfate therein, the voltage rose only slightly above 68 volts and then was depressed by the arc-supporting potassium sulfate. No overloading of the carbons occurred. Thus, it will be manifest that by adding an arc-supporting material to the joint between joined arc carbons, improved operation evidenced by a steady arc is achieved. The invention may also be employed advantageously in joining an arc carbon to a stub of a previously burned arc carbon to eliminate loss of the material in the stub.

We claim:

1. An arc carbon electrode having a shell and a core, said cores having a flame material incorporated therein, adapted to be joined with another are carbon electrode to form an assembly of electrodes suitable for use in an arc lamp, said electrode having a plug on one end, a socket in the other end, and an arc-supporting material disposed in said socket in an amount which provides a substantially steady arc during burning of a joint in said assembly of electrodes.

2. The are carbon electrode defined in claim 1 wherein said arc-supporting material is selected from the grOup consisting of potassium sulfate, calcium fluoride, sodium sulfate and silicon metal.

3. The are carbon electrode defined in claim 1 wherein said arc-supporting material is potassium sulfate.

4. An arc carbon electrode having a shell and a core, said cores having a flame material incorporated therein, adapted to be joined with another are carbon electrode to form an assembly of electrodes suitable for use in an arc lamp, said electrode having a plug on one end, a socket in the other end, and an arc-supporting material disposed on said plug in an amount sufficient to provide a substantially steady arc during burning of a joint in said assembly of electrodes.

5. The arc carbon electrode defined in claim 4 wherein said arc-supporting material is selected from the group consisting of potassium sulfate, calcium fluoride, sodium sulfate and silicon metal.

6. The arc carbon electrode defined in claim 4 wherein said arc-supporting material is potassium sulfate.

7. An assembly of carbon electrodes each electrode having a shell and a core, said core having a flame material incorporated therein, suitable for use in an arc lamp, said assembly comprising a first carbon electrode having a socket in one end, a second carbon electrode having a plug on one end which fits in said socket, and an arcsupporting material disposed in said socket between said plug of said second carbon electrode and said first carbon electrode, said arc-supporting material being present in an amount sufficient to provide a substantially steady arc during burning of the joint between said first carbon electrode and said second carbon electrode in said assembly.

8. The arc carbon electrode assembly defined in claim 7 wherein said arc-supporting material is selected from the group consisting of potassium sulfate, calcium fluoride, sodium sulfate and silicon metal.

9. The are carbon electrode assembly defined in claim 7 wherein said arc-supporting material is potassium sulfate.

References Cited by the Examiner UNITED STATES PATENTS 1,774,964 9/1930 Dewey 3l3354 2,093,390 9/1937 Wyckoff 313357 X 2,229,227 1/1941 Simon et al7 3l3354 2,657,326 10/1953 McCarty 313354 3,048,433 8/1962 Doetsch 174-94 3,187,089 6/1965 Cosby et al. 17494 JOHN W. HUCKERT, Primary Examiner.

A. J. JAMES, Assistant Examiner. 

1. AN ARC CARBON ELECTRODE HAVING A SHELL AND A CORE, SAID CORES HAVING A FLAME MATERIAL INCORPORATED THEREIN, ADAPTED TO BE JOINED WITH ANOTHER ARC CARBON ELECTRODE TO FORM AN ASSEMBLY OF ELECTRODES SUITABLE FOR USE IN AN ARC LAMP, SAID ELECTRODE HAVING A PLUG ON ONE END, A SOCKET IN THE OTHER END, AND AN ARC-SUPPORTING MATERIAL DISPOSED IN SAID SOCKET IN AN AMOUNT WHICH PROVIDES A SUBSTANTIALLY STEADY ARC DURING BURNING OF A JOINT IN SAID ASSEMBLY OF ELECTRODE. 